At a grade intersection, a conflict area is a space which traffic units in different flow directions have to pass. A critical point is the most dangerous point in the conflict area. The traffic units enter into the conflict area in turn according to signal sequence. the movement of a traffic tail unit released when ending a green light i from its stop line to pass through the critical point is referred to as a clearing, and the length of the trace of this movement is referred to as a clearing distance si, the time spend by the movement is a clearing time ti. The movement of a traffic head unit released when starting a green light j from its stop line to the critical point is referred to as an entry, and the length of the trace of this movement is referred to as an entry distance sj, the time spend by the movement is an entry time tj. The road channelization of the intersection can make the traffic units in different flow directions pass along a certain path respectively, so that each of the conflict areas and the critical point positions is relatively fixed.
Motor vehicles which go straight and turn left are referred to a frame vehicle flow for short. A road traffic signal controller is an apparatus which can change the sequences of road traffic signals, adjust timing and control signal operations of traffic signal lights. The road traffic signal controller has therein a parameter setting program for arranging a phase structure and a phase sequence structure of a signal. In order to avoid the traffic confliction, adjoined conflict phase stages are separated by phase intervals which are usually larger than 0; by setting a parameter, for a frame vehicle flow, a time open interval (namely a line segment without endpoints on the time axis), the green lights in which are more than those in a earlier or later time open interval is referred to as a phase stage. Green lights operating in one phase stage are collectively referred to as the same phase structure. A time open interval of a green light signal which is turned off after the end of the phase stage is referred to as a late off stage. A time open interval of a green light signal which is turned on before the start of the phase stage is referred to as an early on stage. A green light which is continuously on during several phase stages is called a cross-stage green light. A phase stage in which a late off stage and an early on stage which overlaps is referred to as an overlapped phase stage. A green light for the non-frame vehicle flow may further have a late on stage or an early off stage. A cycle means that the time needed to alternately show each of all the light colors of the frame vehicle flow signal lights once. If there are more than two phase stages in a cycle, it is referred to as a multi-phase control; and the operation sequence of the phase stages is referred to as a phase sequence structure.
In the case of a phase interval smaller than 0, those concepts can also be unambiguously applied. In order to ensure traffic safety, any phase interval must be greater than or equal to the contained green interval of the frame vehicle flow. The green interval is a security interval to be set between the time when the green light i is turned off and the time when the green light j conflicting with the green light i is turned on. The minimum value of the green interval is referred to as an i-j minimum green interval. The green time must be greater than or equal to the corresponding minimum green time. Three constraints of the traffic signal control system includes the minimum green interval, the minimum green time and the traffic capacity of the intersection.
Since the three constraints can not be determined accurately by all the typical signal control systems, there are disadvantages in the following four technical means. The existing control design methods are completely ineffective in the case of negative cycle loss time.
Firstly, the road channelization is performed with great arbitrariness, since conventionally there is no specific numerical value index to appraise the road channelization. Therefore the road channelization is regarded as an intellectual activity in many countries and isn't granted the patent protection. In order to find the best road channelization technically, this arbitrariness must be changed by establishing logically preferred numerical value indexes and performing engineering and technology screening.
Secondly, the minimum value of the green interval is uniformly set as 4 s or 3 s, in some conventional signal control designs. Thus the minimum green interval is set to be too small, which is neither reasonable nor safe, leading to accident-proneness in the phase interval. Moreover, the traditional phase structure design is task needed to be completed before the timing design. Presently a phase structure scheme is determined mainly by experience judgment or enumeration. No literature can assure that a phase structure scheme therein is the best. In addition, in these classic systems, it is not able to configure a countdown display and it is difficult to reduce the start-up lost time.
FIG. 2 shows an entry flow rate-time curve at the section of a stop line of an intersection. As shown in the curve, due to forbiddance for running the red light, the vehicle flow passing through the stop line doses not reach the saturation flow rate near the time when the yellow light is turned off, and the passage time loss caused by this non-saturation flow rate is referred to as a yellow end loss time. When the green light is turned on, the vehicle flow may be difficult to enter with a saturation flow rate at the beginning, and the passage time loss caused by this non-saturation flow rate is referred to as a green start loss time. The total sum of the green loss time and the yellow end loss time is referred to as a start-up loss time. “According measurements actually carried out in British, the start-up lost time of the motor vehicle flow is 1.48 seconds, and the yellow end loss time is 0.13 seconds”  Beijing: China Communications Press, 1995, P108). Obviously, the start-up lost time is independent of the minimum green interval.
An effective green time of the vehicle flow is the time when the vehicle is released by a saturation flow rate during a cycle, namely:Gej=Gj+A−l=C0λj  (1)
The saturation degree qj of the vehicle flow j is used to describe the congestion level of the frame vehicle flow at the intersection:qj=C0Qj/GejnjQsj=Qj/λjnjQsj≦q  (2)
For the maximum allowable saturation q, each split λj should be greater than or equal to each corresponding required split λj:λj=Qj/qnjQsj  (3)
In the above equation, Gej is the effective green time of the frame traffic flow; Gj is the green time of the traffic flow; A is the yellow light time; l is the start-up loss time; C0 is the cycle; λj is the split, namely the ratio of the effective green time to the cycle: λj=Gei/C0; nj is the number of traffic lanes; q is the maximum allowable saturation degree; Qsj is the saturation flow rate j of the frame vehicle flow in a single traffic lane and is measured in pcu/h; Qj is the actual flow rate of the frame vehicle flow j and is measured in pcu/h; and λj is the required split of the frame vehicle flow.
In determining the cycle and the green light timing, the frame vehicle flow which determines the green time in each phase stage is referred to as a key vehicle flow. The key vehicle flow has a bigger saturation degree except in the case where the green time is equal to the minimum green time. A periodical path which is formed of the key vehicle flow green time interval and the prior or posterior green time intervals connected sequentially is referred to as a key path.
For all the frame vehicle flow which can form a periodical path, the cycle is expressed by the following relational expression where the Ii denotes the green interval:C0=Σ(Gi+Ii)  (4)
A cycle loss time L is the difference between the total sum of the effective green time in the key path and the cycle:L=C0−ΣGei  (5)
In any conventional timing design method, the cycle loss time is an important parameter that must be accurately determined. However, an estimation value which is very inaccurate is commonly used instead. The cycle loss time follows by substituting (4) into (5):L=ΣIi−(A−l)×n  (6)